A diesel particulate filter (DPF) attached to an exhaust pipe for removing particulate matter from the exhaust gas of a diesel engine heats and burns the particulate matter when the trapped particulate matter amount reaches a predetermined amount. This process is known as DPF regeneration.
Tokkai Hei 5-240026, published by the Japan Patent Office in 1993, teaches that the need for regeneration of a DPF is determined according to a differential pressure between the exhaust gas pressure upstream of the DPF and the exhaust gas pressure downstream of the DPF.